Method and apparatus for silicon-based optically-pumped amplification using stimulated scattering

ABSTRACT

A semiconductor-based optical amplifier using optically-pumped stimulated scattering includes an optical signal source (pump) and a wavelength selective coupler. The coupler is connected to receive an input optical signal and the pump signal and output the combined signals in a waveguide having a semiconductor core. The intensity of the pump signal is selected so that stimulated scattering occurs when the pump signal is propagated in the semiconductor core. Further, the wavelength of the pump signal is selected so that the stimulated scattering causes emission of a signal shifted in wavelength to be substantially equal to the wavelength of the optical input signal. Consequently, the input signal is amplified as it propagates with the pump signal. The amplifier can be disposed between reflectors to form a laser.

FIELD OF THE INVENTION

[0001] Embodiments of invention relate generally to optical devices and,more specifically but not exclusively relate to semiconductor-basedoptical amplification.

BACKGROUND INFORMATION

[0002] Amplification of optical signals is often required in opticalcommunication systems. Optical amplifiers can be implemented in opticalfiber such as, for example, erbium doped fiber amplifiers (EDFAs), fiberRaman amplifiers. Such optical amplifiers can be useful in many opticalfiber applications.

[0003] Optical amplifiers can also be implemented in semiconductormaterials (e.g., semiconductor optical amplifiers or SOAs). However,SOAs tend to be low power, noisy and polarization sensitive.

BRIEF DESCRIPTION OF THE DRAWINGS

[0004] Non-limiting and non-exhaustive embodiments of the presentinvention are described with reference to the following figures, whereinlike reference numerals refer to like parts throughout the various viewsunless otherwise specified.

[0005]FIG. 1 is a block diagram illustrating a silicon-based stimulatedRaman scattering (SRS) amplifier, according to one embodiment of thepresent invention.

[0006]FIG. 2 is a graph illustrating the gains of the SRS amplifierdepicted in FIG. 1.

[0007]FIG. 3 is a simplified block diagram of an optical communicationsystem containing the SRS amplifier depicted in FIG. 1.

[0008]FIG. 4 is a block diagram of single pump silicon-based SRSamplifier array, according to one embodiment of the present invention.

[0009]FIG. 5 is a block diagram of a silicon-based SRS laser, accordingto one embodiment of the present invention.

[0010]FIG. 6 is a block diagram of a single pump silicon-based SRSmulti-wavelength laser, according to one embodiment of the presentinvention.

[0011]FIG. 7 is a block diagram of a silicon-based stimulated Brillouinscattering (SBS) laser, according to one embodiment of the presentinvention.

[0012]FIG. 8 is a block diagram of a single pump silicon-based SBSmulti-wavelength multi-output laser, according to one embodiment of thepresent invention.

[0013]FIG. 9 is a block diagram of a single pump silicon-based SBSmulti-wavelength single-output laser, according to one embodiment of thepresent invention.

DETAILED DESCRIPTION

[0014]FIG. 1 illustrates a semiconductor device 100 having disposedthereon a silicon-based stimulated Raman scattering (SRS) amplifier 102,according to one embodiment of the present invention. In thisembodiment, semiconductor device 100 is implemented using a siliconsubstrate 103, and includes optical circuitry 104 that receives anamplified optical signal from SRS amplifier 102. In one embodiment,silicon substrate 103 is part of a silicon on insulator (SOI) wafer. SRSamplifier 102, in this embodiment, includes a pump laser 106 and awavelength selective coupler 107.

[0015] The elements of this embodiment of semiconductor device 100 areinterconnected as follows. Laser 106 has an output port connected to aninput port of wavelength selective coupler 107 via a waveguide 108.

[0016] Wavelength selective coupler 107 has another input port connectedto receive an optical input signal via a waveguide 109. Further, in oneembodiment, waveguide 109 is connected to receive the optical inputsignal via an optical fiber 111. In other embodiments, the optical inputsignal can be received from a source disposed on semiconductor device100.

[0017] Wavelength selective coupler 107 also has an output portconnected to an optical input port of optical circuitry 104 via awaveguide 113. Amplification of the signal occurs in a section ofwaveguide 113. This section of waveguide can be straight or bended.Optical circuitry 104, in one embodiment, has an optical output portconnected to a waveguide 115, which in turn is connected to an opticalfiber 117. In other embodiments, waveguide 113 may be connected directlyto optical fiber 117.

[0018] In this embodiment, waveguides 108, 109, 113 and 115 are eachimplemented in silicon substrate 103 so as to have a silicon core. Inother embodiments, these waveguides may have a core formed from adifferent material or materials.

[0019] In operation, laser 106 provides an optical pump signal for usein amplifying an optical input signal of selected frequency viastimulated Raman scattering (SRS). SRS can occur in a medium propagatingan optical signal of a given frequency (i.e., a pump signal) if theoptical signal exceeds a threshold intensity for that material andfrequency. When SRS occurs in the medium, some of the energy of the pumpsignal is converted to light of a different frequency. This differenceor shift in frequency is called the Stokes frequency shift. For example,in silicon, the first order Stokes frequency is approximately 191.3 THzfor a 1450 nm pump signal. Laser 106 outputs the pump signal ofwavelength λ_(P) via waveguide 108. In one embodiment, laser 106 isimplemented with a laser diode lasing in the 14XX nm wavelength rangeand having a power output ranging from 300-500 mW. Such laser diodes arecommercially available.

[0020] A value for the SRS gain coefficient for a waveguide can be foundby equation 1:

g=16π³ c ² S/(hω_(s) ³ n _(s) ²(N ₀+1))Γ)  (1)

[0021] where S is the spontaneous Raman scattering coefficient(proportional to ω_(s) ⁴), h is Planck's constant, n_(s) is therefractive index of the waveguide core material at the Stoke'sfrequency, ω_(s) is the angular frequency of the Stokes emission, N₀ isthe Bose factor and F is one half the full width at half maximum of theStokes line (in units of angular frequency). Equation 1 (due to theω_(s) ⁴ factor of S) shows that the gain coefficient is linearlydependent on the Stokes frequency.

[0022] Wavelength selective coupler 107 receives an optical input signalof wavelength λ₁ via waveguide 109. In this embodiment, λ₁ is selectedso that its frequency is substantially equal to the first order Stokesfrequency of the pump signal. Wavelength selective coupler 107 couplesthe input signal so that the input signal and the pump signal propagatein waveguide 113. As the input signal propagates with the pump signal,the input signal is amplified via SRS in waveguide 113. The gainprovided by one embodiment of silicon-based SRS amplifier 102 can beestimated described below.

[0023] Experimental data is published for SRS in silicon at 77°K, aλ_(P) of 1064 nm and scattering in the [111] crystalline axis of thesilicon. Using this experimental data, the SRS gain coefficient forsilicon using current telecommunication operating parameters can bepredicted. For example, telecommunication systems typically operate atroom temperature, with pump light having a wavelength in the 14XX nmrange. In addition, optical signal propagation in silicon devices istypically in the [100] and [110] crystalline axes instead of [111] as inthe experimental data.

[0024] Using these parameters and determining correction factors forthese parameters from the experimental data, the gain coefficient can beestimated. For example, at 77°K, (N₀+1)=1 from the experimental data.Correcting for the change in line width and Bose factor due totemperature, at 300°K, (N₀+1)=1.088. As previously mentioned, the Ramangain is linearly dependent on the Stokes frequency. The gain coefficientfrom the experimental data (i.e., wavelength of 1064 nm) is multipliedby 0.718 and 0.674, respectively for embodiments using 1450 nm and 1535pump wavelengths. In addition, for propagation along the [110] and [100]axes of silicon the conversion efficiency is about 90% of the conversionefficiency for propagation along the [111] axis of the experimentaldata.

[0025] Using the correction factors above, the gain coefficient atcurrent telecommunications temperatures and frequencies can be estimatedat about 4×10⁻⁸ cm/W. FIG. 2 illustrates this gain coefficient withvarious values of waveguide loss. As shown in FIG. 2, the expected gainper unit length is linear with pump signal intensity. Thus, the lengthof waveguide 113 is selected to achieve the desired gain. In otherembodiments, the temperature, refractive index and other parameters maybe adjusted to achieve the desired gain.

[0026] The amplified optical signal is then received by opticalcircuitry 104, which then operates on the amplified signal. For example,optical circuitry 104 may include an array waveguide grating (AWG) toseparate out the amplified input signal from the residual pump signal.

[0027] Since this embodiment of SRS amplifier 102 is implemented insilicon, SRS 102 can be advantageously integrated with othersilicon-based optical circuitry (e.g., lasers, couplers, filters,gratings, receivers, transmitters, etc.) in a single monolithic deviceor chip. By integrating these optical components, significantimprovements in performance and cost can be achieved. For example, insome conventional systems, non-silicon optical amplifiers would requirehybrid packaging with typical silicon die, which can significantlyincrease cost, complexity, size (e.g., pitch) and signal loss.

[0028]FIG. 3 illustrates an exemplary optical communication system 300containing SRS amplifier 102 (FIG. 1). In this exemplary embodiment,system 300 includes an optical signal source 301 and a planar lightwavecircuit (PLC) 303 formed from silicon. In this embodiment, PLC 303includes an optical filter 311, an optical receiver 313, an opticalcoupler 315, an optical transmitter 317 and optical circuitry 319. Inthis example, these elements of PLC 303 are used to implement an opticaladd/drop multiplexer.

[0029] The above elements of this embodiment of system 300 areinterconnected as follows. Optical signal source 301 is connected to PLC303 via optical fiber 111. Optical filter 311 has an input portconnected to receive an optical signal from optical fiber 111 viawaveguide 321. Optical filter 311 has an output port connected to theinput port of SRS amplifier 102 via a waveguide 323, which in turn hasits output port connected to an input port of optical receiver 313 via awaveguide 325. Optical filter 311 has another output port connected toan input port of coupler 315 via a waveguide 327. Coupler 315 hasanother input port connected to an output port of transmitter 317 via awaveguide 329, and has an output port connected to an input port ofoptical circuitry 319 via a waveguide 331. In this embodiment, opticalcircuitry 319 has an output port connected to optical fiber 117 via awaveguide 333. In other embodiments, waveguide 331 may be directly tooptical fiber 117, bypassing optical circuitry 319.

[0030] This example system operates as follows. Optical signal source301 is part of a WDM optical system, providing a multi-wavelengthoptical input signal (including λ₁ as shown in FIG. 1) for PLC 303.Optical filter 311 filters out a selected wavelength of the inputsignal. In this embodiment, optical filter 311 filters out the λ₁wavelength, which SRS amplifier 102 amplifies as described above usingSRS. The remaining wavelengths of the input signal are passed by opticalfilter 311 to coupler 315.

[0031] The amplified signal is then received by receiver 313 andconverted to an electronic signal for processing by other units (notshown) of PLC 303. For example, the electronic signal can be provided toa processor (not shown) that extracts information modulated on the λ₁wavelength signal.

[0032] Transmitter 317 outputs an optical signal of wavelength λ₁ tocoupler 315. In this embodiment, the λ₁ wavelength signal is modulatedwith information for transmission to another unit of system 300. Coupler315 combines the signal from transmitter 317 with the residual opticalsignal from optical filter 311 and outputs the combined signals ontowaveguide 331. The combined signals can then be processed (e.g.,amplified) and transmitted out of PLC 303 via waveguide 333 and opticalfiber 117.

[0033]FIG. 4 illustrates a single pump silicon-based SRS amplifier array400, according to one embodiment of the present invention. Thisembodiment is similar to SRS amplifier 102 (FIG. 1), with the additionof dual wavelength selective couplers 402 and 404, which are alsoimplemented in silicon substrate 103.

[0034] The above elements of array 400 are interconnected as follows.Coupler 402 has one input port connected to the output port of coupler107 via waveguide 113 and another input port connected to receive aninput signal of wavelength λ₂ via a waveguide 408. Coupler 402 has oneoutput port connected to a waveguide 409 and another output portconnected to a waveguide 410. Coupler 404 has one input port connectedto waveguide 410 and another input port connected to receive an inputsignal of wavelength λ₃ via a waveguide 412. Coupler 404 has one outputport connected to a waveguide 413 and another output port connected to awaveguide 414.

[0035] In operation, laser 106 outputs the pump signal of wavelengthλ_(P) to coupler 107 to be used in amplifying the λ₁ input signal asdescribed above in conjunction with FIG. 1. The amplified λ₁ signalalong with the residual pump signal propagates to coupler 402 viawaveguide 113.

[0036] Coupler 402 is a dual wavelength selective coupler, causing theamplified signal of wavelength λ₁ to propagate in waveguide 409 whilecausing the input signal of wavelength λ₂ and the residual pump signalto propagate in waveguide 410. Laser 106 provides the pump signal withenough power so that SRS scattering occurs in waveguide 410 (and 414)after the λ₁ (and λ₂) input signal is amplified. Thus, SRS occurs inwaveguide 410, which can then be used to amplify the λ₂ input signal.Note, although the λ₁ input signal is at the Stokes frequency, theStokes frequency represents the frequency at which the peak intensityemission occurs. Depending on the medium, a finite range of frequenciescentered on the Stokes frequency is also emitted and can be used foramplifying signals with wavelengths within this range. In thisembodiment, λ₂ is selected to be within the range of SRS emissions forsilicon so that the λ₂ input signal is amplified as it propagates inwaveguide 410 along with the residual pump signal.

[0037] Coupler 404 is also a dual wavelength selective coupler. Thus,coupler 404 similarly causes the amplified λ₂ signal to propagate inwaveguide 413 while causing the input signal of wavelength λ₃ and theresidual pump signal to propagate in waveguide 414. In this embodiment,λ₃ is also selected to be within the range of SRS emissions for siliconso that the λ₃ input signal is amplified as it propagates in waveguide410 along with the residual pump signal.

[0038]FIG. 5 illustrates a silicon-based SRS laser 500, according to oneembodiment of the present invention. In this embodiment, laser 500includes a narrow line width pump laser 502, a wavelength selectivecoupler 504, reflectors 506 and 508 and waveguides 510, 512 and 514.Waveguides 510, 512 and 514 have cores formed from the silicon substrate103.

[0039] Pump laser 502 has an output port connected to one port ofcoupler 514 via waveguide 510. Coupler 504 also has ports connected toreflectors 506 and 508 via waveguides 512 and 514, respectively. In oneembodiment, reflectors 506 and 508 are Bragg gratings disposed insilicon (e.g., by alternating regions of silicon and another material ofdifferent refractive index). In other embodiments, different reflectorimplementations can be used. In this embodiment, the reflectors areselected to have a relatively high reflectivity for the Stokes linesignal, with one being slightly less to serve as an output port. Inaddition, reflectors 506 and 508 are selected to have relatively hightransmission at the pump wavelength.

[0040] In operation, one embodiment of pump laser 502 is a laser diodelasing at 1455 nm with an intensity sufficient to cause SRS in silicon,which results in a Stokes line at 1574 nm. Reflectors 506 and 508, inthis embodiment, are narrow band reflectors that are highly reflectiveat 1574 nm. Therefore, a laser is formed that outputs a 1574 nm signal.In other embodiments, the reflectors may be narrow band reflectors atdifferent wavelengths, but within the emission range of SRS of thesilicon of silicon substrate 103. This configuration can also be used asa wavelength converter, converting a signal of the pump wavelength toone of the Stokes shifted wavelength.

[0041] In an alternative embodiment, the reflectors can be tunable inreflective wavelength, thereby allowing the laser output signal to havea tunable wavelength within the aforementioned finite range about theStokes wavelength. For example, the reflectors can be implemented usingtunable Bragg gratings.

[0042]FIG. 6 illustrates a single pump silicon-based SRSmulti-wavelength laser 600, according to one embodiment of the presentinvention. This embodiment is similar to laser 500 (FIG. 5) with theaddition of four pairs of narrow band reflectors 604A/604B, 606A/606B,608A/608B, 610A/610B and 612A/612B. Each pair of reflectors has adifferent reflection wavelength within the emission range of SRS insilicon. In addition, laser 600 includes wavelength selective couplers614, 616, 618, and 620.

[0043] In this embodiment, the above reflectors are Bragg gratingsformed in waveguides having cores formed from silicon substrate 103.

[0044] In operation, reflectors 604A and 604B, coupler 614 and laserpump 602 form a laser substantially similar to laser 500 (FIG. 5) withlaser output at wavelength λ₁ at an output waveguide 624.

[0045] Coupler 614 also causes the residual pump signal to propagate toreflectors 606A and 606B formed in a waveguide connected to coupler 616.Reflectors 606A and 606B form a laser that lases at wavelength λ₂, whichcoupler 616 outputs at a waveguide 626.

[0046] The residual pump signal propagates to reflectors 608A and 608Bformed in a waveguide connected to reflector 606A. Reflectors 608A and608B form a laser that lases at wavelength λ₃, which coupler 618 outputsat a waveguide 628. Coupler 618 also causes the residual pump signal topropagate to reflectors 610A and 610B formed in a waveguide connected tocoupler 618.

[0047] Reflectors 610A and 610B form a laser that lases at wavelengthλ₄, which coupler 620 outputs at a waveguide 630. The residual pumpsignal propagates to reflectors 612A and 612B formed in a waveguideconnected to reflector 610A. Reflectors 612A and 612B form a laser thatlases at wavelength λ₅, which is output via a waveguide 632. Pump laser602 outputs the pump signal with sufficient intensity to cause SRS inthe waveguides between all of the reflector pairs.

[0048]FIG. 7 illustrates a silicon-based stimulated Brillouin scattering(SBS) laser 700, according to one embodiment of the present invention.SBS is similar to SRS in that a pump signal exceeding a thresholdintensity will cause SBS to occur in certain mediums. In one embodiment,the shifted SBS frequency is approximately 50 GHz in silicon. In SBS,the intensity of the shifted signal has a maxima in the oppositedirection opposite that of the pump signal (unlike SRS). SBS laser 700includes a narrow linewidth pump laser 702 and reflectors 704A and 704Bformed in a waveguide 706 propagating the pump signal from pump laser702. Reflectors 704A and 704B are narrow band reflectors that are highlyreflective for the wavelength of the SBS shifted signal and highlytransmissive for the wavelength of the pump signal.

[0049]FIG. 8 illustrates a single pump silicon-based SBSmulti-wavelength multi-output laser 800, according to one embodiment ofthe present invention. In this embodiment, laser 800 includes reflectorpairs 804A/804B, 806A/806B, 808A/808B, 810A/810B and 812A/812B, and tapcouplers 814, 816, 818 and 820. Reflector pairs 804A/804B, 806A/806B,808A/808B, 810A/810B and 812A/812B are formed to be highly reflective atwavelengths λ₁, λ₂, λ₃, λ₄ and λ₅, respectively, while allowing otherwavelengths to pass.

[0050] Pump laser 802 and reflectors 804A and 804B generate a λ₁wavelength SBS laser signal as described above in conjunction with FIG.7. Tap coupler 814 taps a portion of the λ₁ laser signal to an outputwaveguide 824, while propagating the rest of the λ₁ laser signal toreflectors 806A and 806B. This portion of the λ₁ laser signal serves asthe pump signal for the λ₂ laser formed by reflectors 806A and 806B.

[0051] Tap coupler 816 taps a portion of the λ₂ laser to an outputwaveguide 826, while propagating the rest of the λ₂ laser signal toreflectors 808A and 808B to serve as the pump signal for the λ₃ laserformed by reflectors 808A and 808B.

[0052] Tap coupler 818 taps a portion of the λ₃ laser to an outputwaveguide 828, while propagating the rest of the λ₃ laser signal toreflectors 810A and 810B to serve as the pump signal for the λ₄ laserformed by reflectors 810A and 810B.

[0053] Tap coupler 820 taps a portion of the λ₄ laser to an outputwaveguide 830, while propagating the rest of the λ₄ laser signal toreflectors 812A and 812B to serve as the pump signal for the λ₅ laserformed by reflectors 812A and 812B.

[0054]FIG. 9 illustrates a single pump silicon-based SBSmulti-wavelength single-output laser 900, according to one embodiment ofthe present invention. In this embodiment, laser 900 includes threepairs of narrow band reflectors 904A/904B, 906A/906B and 908A/908Bformed in silicon substrate 103 to have silicon cores. Reflectors904A/904B, 906A/906B and 908A/908B are highly reflective at wavelengthsλ₁, λ₂, and λ₃, respectively, while allowing other wavelengths to pass.In this embodiment, reflectors 904A and 904B are disposed outside ofreflectors 906A and 906B, which in turn are disposed outside ofreflectors 908A and 908B. In this way, Reflectors 904A/904B, 906A/906Band 908A/908B respectively form lasers of wavelengths λ₁, λ₂, and λ₃,which are output on a single waveguide. The different laser signals canbe separated with other optical circuitry such as an AWG (not shown) asrequired.

[0055] Embodiments of method and apparatus for SRS and SBS amplifiers,lasers and wavelength converters are described herein. In the abovedescription, numerous specific details are set forth to provide athorough understanding of embodiments of the invention. One skilled inthe relevant art will recognize, however, that embodiments of theinvention can be practiced without one or more of the specific details,or with other methods, components, materials, etc. In other instances,well-known structures, materials, or operations are not shown ordescribed in detail to avoid obscuring the description.

[0056] Reference throughout this specification to “one embodiment” or“an embodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the present invention. Thus, theappearances of the phrases “in one embodiment” or “in an embodiment” invarious places throughout this specification are not necessarily allreferring to the same embodiment. Furthermore, the particular features,structures, or characteristics may be combined in any suitable manner inone or more embodiments.

[0057] In addition, embodiments of the present description may beimplemented not only within a semiconductor chip but also withinmachine-readable media. For example, the designs described above may bestored upon and/or embedded within machine readable media associatedwith a design tool used for designing semiconductor devices. Examplesinclude a netlist formatted in the VHSIC Hardware Description Language(VHDL) language, Verilog language or SPICE language. Some netlistexamples include: a behavioral level netlist, a register transfer level(RTL) netlist, a gate level netlist and a transistor level netlist.Machine-readable media also include media having layout information suchas a GDS-II file. Furthermore, netlist files or other machine-readablemedia for semiconductor chip design may be used in a simulationenvironment to perform the methods of the teachings described above.

[0058] Thus, embodiments of this invention may be used as or to supporta software program executed upon some form of processing core (such asthe CPU of a computer) or otherwise implemented or realized upon orwithin a machine-readable medium. A machine-readable medium includes anymechanism for storing or transmitting information in a form readable bya machine (e.g., a computer). For example, a machine-readable medium caninclude such as a read only memory (ROM); a random access memory (RAM);a magnetic disk storage media; an optical storage media; and a flashmemory device, etc. In addition, a machine-readable medium can includepropagated signals such as electrical, optical, acoustical or other formof propagated signals (e.g., carrier waves, infrared signals, digitalsignals, etc.).

[0059] The above description of illustrated embodiments of theinvention, including what is described in the Abstract, is not intendedto be exhaustive or to be limitation to the precise forms disclosed.While specific embodiments of, and examples for, the invention aredescribed herein for illustrative purposes, various equivalentmodifications are possible, as those skilled in the relevant art willrecognize.

[0060] These modifications can be made to embodiments of the inventionin light of the above detailed description. The terms used in thefollowing claims should not be construed to limit the invention to thespecific embodiments disclosed in the specification and the claims.Rather, the scope is to be determined entirely by the following claims,which are to be construed in accordance with established doctrines ofclaim interpretation.

What is claimed is:
 1. An apparatus, comprising: a waveguide disposed ina semiconductor material to receive a first optical signal of a firstwavelength and having a first power level, wherein the first power levelis sufficient to cause emission of a second optical signal of a secondwavelength when the first optical signal is propagated in the waveguide;and a coupler to receive the first optical signal and an input opticalsignal having a third wavelength different from the first wavelength,the coupler to cause an optical output signal to propagate in thewaveguide, the optical output signal including at least parts of theinput signal and the first optical signal.
 2. The apparatus of claim 1wherein the semiconductor material comprises silicon, and wherein thewaveguide's core is silicon.
 3. The apparatus of claim 1 wherein thethird wavelength and second wavelength are substantially equal.
 4. Theapparatus of claim 1 wherein the third wavelength of the input signal isamplified as it propagates through the waveguide.
 5. The apparatus ofclaim 4 wherein a gain of the amplification increases linearly with thewaveguide's length.
 6. The apparatus of claim 1 further comprisingoptical circuitry, disposed in the semiconductor material, to receivethe optical output from the coupler.
 7. The apparatus of claim 1 whereinthe coupler is a wavelength selective coupler disposed in thesemiconductor material.
 8. The apparatus of claim 1 further comprising alaser disposed in the semiconductor material to provide the firstoptical signal.
 9. The apparatus of claim 1 wherein the first opticalsignal causes stimulated Raman scattering (SRS) in the waveguide. 10.The apparatus of claim 9 wherein the input signal has a frequency thatis substantially equal to a Stokes frequency of the SRS that occurs inthe waveguide.
 11. The apparatus of claim 1 wherein the first opticalsignal causes stimulated Brillouin scattering (SBS) in the waveguide.12. The apparatus of claim 11 wherein the input signal has a frequencythat is substantially equal to a Brillouin frequency of the SBS thatoccurs in the waveguide.
 13. The apparatus of claim 1 further comprisingfirst and second reflectors disposed in the waveguide, the first andsecond reflectors being reflective for the third wavelength.
 14. Theapparatus of claim 13 wherein the first and second reflectors aregratings.
 15. The apparatus of claim 14 wherein the gratings eachinclude a plurality of parallel regions of non-semiconductor materialformed in the waveguide.
 16. The apparatus of claim 13 furthercomprising third and fourth reflectors coupled to the waveguide that arereflective at a fourth wavelength different from the third wavelength.17. A method comprising propagating a first optical signal in awaveguide having a core formed in a semiconductor material, the firstoptical signal having a first wavelength and a first power level,wherein the first power level is sufficiently great to cause a secondoptical signal of a second wavelength to propagate in the waveguide; andcoupling an optical input signal with the first optical signal, theinput signal having a third wavelength different from the firstwavelength.
 18. The method of claim 17 wherein the semiconductormaterial comprises silicon.
 19. The method of claim 17 wherein thesecond and third wavelengths are substantially equal.
 20. The method ofclaim 17 wherein the third wavelength of the optical input signal isamplified as it propagates through the waveguide.
 21. The method ofclaim 20 wherein a gain of the amplification increases linearly with thewaveguide's length.
 22. The method of claim 20 wherein the first opticalsignal causes stimulated Raman scattering (SRS) in the waveguide. 23.The method of claim 22 wherein the optical input signal has a frequencythat is equal to a Stokes frequency of the SRS that occurs in thewaveguide.
 24. The method of claim 20 wherein the first optical signalcauses stimulated Brillouin scattering (SBS) in the waveguide.
 25. Themethod of claim 24 wherein the optical input signal has a frequency thatis equal to a Brillouin frequency of the SBS that occurs in thewaveguide.
 26. The method of claim 20 wherein the waveguide includesfirst and second reflectors disposed in the waveguide.
 27. The method ofclaim 26 further comprising third and fourth reflectors coupled to thewaveguide.
 28. The method of claim 26 wherein the first and secondreflectors are gratings.
 29. The method of claim 28 wherein each gratingincludes a plurality of parallel regions of non-semiconductor materialformed in the waveguide.
 30. A system comprising: an optical signalsource to output a first optical signal of a first wavelength; asemiconductor device to receive the first optical signal, thesemiconductor device including: a waveguide disposed in semiconductormaterial of the semiconductor device to receive a second optical signalof a second wavelength different from the first wavelength, the secondoptical signal having an intensity that is sufficient to cause emissionof a third optical signal of a third wavelength different from thesecond wavelength when the second optical signal is propagated in thewaveguide; and a coupler disposed in semiconductor material of thesemiconductor device to receive the first and second optical signals,the coupler to cause an optical output signal to propagate in thewaveguide, the optical output signal including at least parts of thefirst and second optical signals.
 31. The system of claim 30 wherein thesemiconductor device comprises a silicon substrate, and wherein thewaveguide's core is silicon.
 32. The system of claim 30 wherein thefirst and third wavelengths are substantially equal.
 33. The system ofclaim 30 wherein the first wavelength of the first optical signal isamplified as it propagates through the waveguide.
 34. The system ofclaim 30 wherein a gain of the amplification increases linearly with thewaveguide's length.
 35. The system of claim 30 wherein the semiconductordevice further comprises optical circuitry disposed in semiconductormaterial of the semiconductor device to receive the optical output fromthe coupler.
 36. The system of claim 30 wherein the coupler is awavelength selective coupler.
 37. The system of claim 30 furthercomprising a laser integrated on the semiconductor device to provide thesecond optical signal.
 38. The system of claim 30 wherein the secondoptical signal causes stimulated Raman scattering (SRS) in thewaveguide.
 39. The system of claim 38 wherein the first optical signalhas a frequency that is substantially equal to a Stokes frequency of SRSthat occurs in the waveguide.
 40. The system of claim 30 wherein thesecond optical signal causes stimulated Brillouin scattering (SBS) inthe waveguide.
 41. The system of claim 30 wherein the first opticalsignal has a frequency that is substantially equal to a Brillouinfrequency of SBS that occurs in the waveguide.
 42. The system of claim30 wherein the semiconductor device includes first and second reflectorsdisposed in the waveguide.
 43. The system of claim 42 further comprisingthird and fourth reflectors coupled to the waveguide.
 44. The system ofclaim 42 wherein the first and second reflectors are gratings.
 45. Thesystem of claim 44 wherein each grating includes a plurality of parallelregions of non-semiconductor material formed in the waveguide.